1. Field of the Invention
The present invention relates to variable focus lens systems having both automatic and manual focusing means in general, and to such lens systems for photographic cameras, in particular.
2. Description of the Prior Art
Variable focus lens systems having coupled rangefinders, such as those found in certain photographic cameras, are well known in the prior art. The most widely used coupled rangefinder is that of the manually actuated optical type that uses triangulation to determine the distance to the subject to be photographed, which is more commonly referred to as subject distance. Coupled rangefinders that automatically determine subject distance by utilizing radiant or acoustical energy reflected from said subject and then transfer or couple the distance derived by such means to the variable focus lens system of a camera to position said lens system to the correct in-focus position, are also known in the prior art. One such automatic system utilizing reflected acoustical energy is described in U.S. Pat. No. 3,522,764 to BIBER et al.
When utilizing a lens focusing system of the type described in the above-mentioned patent, certain conditions may exist that could render such a focusing system ineffective. For example, an acoustical rangefinder cannot effectively focus the variable focus lens system of a camera on a subject to be photographed if such a subject is separated from the camera by a windowpane, especially of such a pane was in relatively close proximity to said camera and said subject was relatively remote. This problem is briefly mentioned in the above-mentioned BIBER et al. patent at column 8, lines 4-6. In such a situation, acoustical energy would be reflected from the windowpane, incorrectly indicating that the subject distance was substantially less than its true distance. This erroneous distance information supplied by the acoustical rangefinder would then cause the variable focus lens system to form an out-of-focus image at its focal plane which, in the case of a camera, would result in an out-of-focus photograph. This problem could be avoided if the variable focus lens system or camera having such a system had both manual and automatic focus controls. A manually operated optical type coupled rangefinder, for example, is not rendered ineffective if utilized to focus on a subject through transparent media such as a windowpane.
If a variable focus lens system and, specifically, a variable focus lens system in a photographic camera, has both manual and automatic focus controls as mentioned above, wherein said focus controls are mechanically coupled to one another in a driving relationship, intentional or unintentional actuation of the manual focus actuating means while automatically focusing said variable focus lens system may interfere with the automatic focus control system's ability to correctly focus said camera and, in addition, such actuation of the manual focus control system may overstress structural components of both focusing systems. Simultaneous actuation of the manual and automatic focus control systems can be avoided if the manual focus actuating means is provided with a protective barrier or cover that impedes access to said manual focus actuating means. Such a cover would have to be displaced before the manual focus system could be actuated.
One such arrangement is described in U.S. patent application Ser. No. 833,581 by OSTROWSKI et al. filed on the same date and having the same assignee as the present application. In said OSTROWSKI et al. application, a variable focus lens system having mechanically coupled manual and automatic focus controls is disclosed. Simultaneous actuation of the manual and automatic focus control systems is avoided by providing the manual focus actuating means with a displaceable protective cover which impedes access to said manual focus actuating means. While this arrangement is quite effective in terms of avoiding such simultaneous actuation, it does so with structure that is not compatible with a minimum size housing with its attendant cost advantages. Minimum housing size could be achieved if the entire manual focus actuating means and a protective cover for said manual focus actuating means, together with actuating means for said protective cover, were mounted for rotation about the principal image forming axis of said variable focus objective lens. The manual focus actuator and its associated displaceable cover could be included within a housing that conformed to the general shape of the housing enclosing said variable focus objective lens.
Actuation of said displaceable cover could be accomplished by the rotation of a lens shield that is mounted for rotation about the principal image forming axis of said lens system and is coupled to said cover. If such a lens shield projected well beyond the housing of said variable focus lens system, it would be readily accessible for manual actuation.